Split winglet system

Abstract

A winglet system for an aircraft wing includes an upper winglet and a lower winglet mounted to a wing. The lower winglet has a static position when the wing is subject to an on-ground static loading. The lower winglet is configured such that upward deflection of the wing under an approximate 1-g flight loading causes the lower winglet to move upwardly and outwardly from the static position to an in-flight position resulting in an effective span increase of the wing under the approximate 1-g flight loading relative to the span of the wing under the on-ground static loading. The lower winglet is configured to aeroelastically deflect upwardly under the approximate 1-g flight loading and further increase the effective span of the wing beyond the effective span increase that is caused by the upward deflection of the wing.

What is claimed is: 
     
       1. A winglet system, comprising:
 an upper winglet and a lower winglet mounted to a wing; 
 the lower winglet having a static position when the wing is subject to an on-ground static loading; 
 the lower winglet being configured such that upward deflection of the wing under an approximate 1-g flight loading causes the lower winglet to move upwardly and outwardly from the static position to an in-flight position resulting in an effective span increase of the wing under the approximate 1-g flight loading relative to the span of the wing under the on-ground static loading; and 
 the lower winglet being configured to aeroelastically deflect upwardly under the approximate 1-g flight loading and further increase the effective span of the wing beyond the effective span increase that is caused by the upward deflection of the wing. 
 
     
     
       2. The winglet system of  claim 1 , wherein:
 the wing has a wing tip including a wing tip chord; 
 the upper winglet and the lower winglet each having a root chord; and 
 the upper winglet root chord and the lower winglet root chord each have a length of at least approximately 50 percent of the wing tip chord. 
 
     
     
       3. The winglet system of  claim 2 , wherein:
 the upper winglet root chord and the lower winglet root chord each have a length of from approximately 60 to 100 percent of a length of the wing tip chord. 
 
     
     
       4. The winglet system of  claim 1 , wherein:
 at least one of the upper winglet and lower winglet has a leading edge root glove mounted at a juncture of the wing with the respective upper winglet and lower winglet. 
 
     
     
       5. The winglet system of  claim 1  wherein:
 the lower winglet has a length of at least approximately 50 percent of a length of the upper winglet. 
 
     
     
       6. The winglet system of  claim 1  wherein:
 the upper winglet is oriented at a dihedral angle of at least approximately 60 degrees during upward deflection of the wing under the approximate 1-g flight loading. 
 
     
     
       7. The winglet system of  claim 1 , wherein:
 an upper winglet tip and a lower winglet tip terminate at approximately the same lateral location when the wing is under the on-ground static loading. 
 
     
     
       8. The winglet system of  claim 1 , wherein:
 the upper winglet and the lower winglet each have a taper ratio of tip chord to root chord in a range of from approximately 0.15 to 0.50. 
 
     
     
       9. The winglet system of  claim 1 , wherein:
 the upper winglet and the lower winglet have a leading edge sweep angle of between approximately 20 and 70 degrees. 
 
     
     
       10. The winglet system of  claim 1  wherein:
 the lower winglet has a center of pressure; 
 the wing having a wing torsional axis; and 
 the center of pressure of the lower winglet being located aft of the wing torsional axis. 
 
     
     
       11. An aircraft, comprising:
 a pair of wings each having a wing tip; 
 an upper winglet and a lower winglet mounted to each one of the wing tips; 
 the lower winglet on each wing having a static position when the wing is subject to an on-ground static loading; 
 the lower winglet on each wing being configured such that upward deflection of the wing under an approximate 1-g flight loading causes the lower winglet to move upwardly and outwardly from the static position to an in-flight position resulting in an effective span increase of the wing under the approximate 1-g flight loading relative to the span of the wing under the on-ground static loading; and 
 the lower winglet being configured to aeroelastically deflect upwardly under the approximate 1-g flight loading and further increase the effective span of the wing beyond the effective span increase that is caused by the upward deflection of the wing. 
 
     
     
       12. A method of enhancing performance of an aircraft, comprising the steps of:
 providing an upper winglet and a lower winglet on a wing tip of a wing, the lower winglet having a static position when the wing is subject to an on-ground static loading; 
 upwardly deflecting the wing under an approximate 1-g flight loading; 
 moving the lower winglet upwardly and outwardly from the static position to an in-flight position during upward deflection of the wing; 
 causing an effective span increase of the wing under the approximate 1-g flight loading relative to the span of the wing under the on-ground static loading in response to moving the lower winglet upwardly and outwardly from the static position to the in-flight position; and 
 aeroelastically deflecting each lower winglet upwardly under the approximate 1-g flight loading and further increase the effective span of the wing beyond the effective span increase that is caused by the upward deflection of the wing. 
 
     
     
       13. The method of  claim 12 , wherein:
 the wing has a wing tip including a wing tip chord; 
 the upper winglet and the lower winglet each having a root chord; and 
 the upper winglet root chord and the lower winglet root chord each have a length of at least approximately 50 percent of the wing tip chord. 
 
     
     
       14. The method of  claim 13 , wherein:
 the upper winglet root chord and the lower winglet root chord each have a length of from approximately 60 to 100 percent of a length of the wing tip chord. 
 
     
     
       15. The method of  claim 12 , further comprising the step of:
 minimizing parasitic drag of the aircraft by using a leading edge root glove on at least one of the upper winglet and the lower winglet. 
 
     
     
       16. The method of  claim 12 , further comprising the step of:
 providing the upper winglet and the lower winglet with a combined winglet area and a combined center of gravity that is longitudinally offset from a wing torsional axis; and 
 reducing wing flutter by longitudinally offsetting the combined center of gravity by an amount that is less than a longitudinal offset of a center of gravity of a single upper winglet having a winglet area that is substantially equivalent to the combined winglet area and having a leading edge sweep angle that is substantially equivalent to the upper winglet leading edge sweep angle. 
 
     
     
       17. The method of  claim 12 , further comprising the step of:
 orienting the upper winglet at a dihedral angle of at least approximately 60 degrees during the upward deflection of the wing under the approximate 1-g flight loading. 
 
     
     
       18. The method of  claim 12 , wherein:
 an upper winglet tip and a lower winglet tip terminate at approximately the same lateral location when the wing is under the on-ground static loading. 
 
     
     
       19. The method of  claim 12 , further comprising the steps of:
 locating the lower winglet such that a center of pressure is aft of a wing torsional axis; 
 increasing lift of the lower winglet during a gust load; and 
 exerting a nose-down moment on a wing tip in response to an increase in the lift of the lower winglet. 
 
     
     
       20. The method of  claim 12 , further comprising the step of:
 dividing a wing tip aerodynamic load between the upper winglet and the lower winglet.